Signatures of epitaxial graphene grown on Si-terminated 6H-SiC (0001) (original) (raw)
Related papers
Thin Solid Films
Graphene layer grown on different substrates "SiO2 (300 nm)/Si, Si, quartz, glass, NiFe..." has been previously investigated revealed a high dependence on the used substrate. Therefore, the understanding of the substrate effects is still fundamental for future graphene applications. In this work, we report Raman spectroscopy analysis of optical properties of graphene layers grown on different SiC substrates poly type all face terminated C: (3C-SiC (100)/ Si (100), 4H-SiC (000 1 ) and 6H-SiC (000 1 ). Local mapping of Raman spectra have been analysed, where the substrates, the graphene layer's number, the degree of disorder and polarization effect have been identified. We showed strong depends of both SiC substrate and graphene modes to the polarization effect.
Evidence of Structural Strain in Epitaxial Graphene Layers on 6H-SiC(0001)
Physical Review Letters, 2008
The early stages of epitaxial graphene layer growth on the Si-terminated 6H-SiC(0001) are investigated by Auger electron spectroscopy (AES) and depolarized Raman spectroscopy. The selection of the depolarized component of the scattered light results in a significant increase in the C-C bond signal over the second order SiC Raman signal, which allows to resolve submonolayer growth, including individual, localized C=C dimers in a diamond-like carbon matrix for AES C/Si ratio of ∼3, and a strained graphene layer with delocalized electrons and Dirac single-band dispersion for AES C/Si ratio >6. The linear strain, measured at room temperature, is found to be compressive, which can be attributed to the large difference between the coefficients of thermal expansion of graphene and SiC. The magnitude of the compressive strain can be varied by adjusting the growth time at fixed annealing temperature.
Nanoscale Research Letters, 2011
Micro-Raman and micro-transmission imaging experiments have been done on epitaxial graphene grown on the C-and Si-faces of on-axis 6H-SiC substrates. On the C-face it is shown that the SiC sublimation process results in the growth of long and isolated graphene ribbons (up to 600 μm) that are strain-relaxed and lightly p-type doped. In this case, combining the results of micro-Raman spectroscopy with micro-transmission measurements, we were able to ascertain that uniform monolayer ribbons were grown and found also Bernal stacked and misoriented bilayer ribbons. On the Si-face, the situation is completely different. A full graphene coverage of the SiC surface is achieved but anisotropic growth still occurs, because of the step-bunched SiC surface reconstruction. While in the middle of reconstructed terraces thin graphene stacks (up to 5 layers) are grown, thicker graphene stripes appear at step edges. In both the cases, the strong interaction between the graphene layers and the underlying SiC substrate induces a high compressive thermal strain and n-type doping.
Raman spectroscopy of epitaxial graphene on a SiC substrate
Physical Review B, 2008
The fabrication of epitaxial graphene (EG) on SiC substrate by annealing has attracted a lot of interest as it may speed up the application of graphene for future electronic devices. The interaction of EG and the SiC substrate is critical to its electronic and physical properties. In this work, Raman spectroscopy was used to study the structure of EG and its interaction with SiC substrate. All the Raman bands of EG blue shift from that of bulk graphite and graphene made by micromechanical cleavage, which was attributed to the compressive strain induced by the substrate. A model containing 13 × 13 honeycomb lattice cells of graphene on carbon nanomesh was constructed to explain the origin of strain. The lattice mismatch between graphene layer and substrate causes the compressive stress of 2.27 GPa on graphene.
Multiscale investigation of graphene layers on 6H-SiC(000-1)
Nanoscale Research Letters, 2011
In this article, a multiscale investigation of few graphene layers grown on 6H-SiC(000-1) under ultrahigh vacuum (UHV) conditions is presented. At 100-μm scale, the authors show that the UHV growth yields few layer graphene (FLG) with an average thickness given by Auger spectroscopy between 1 and 2 graphene planes. At the same scale, electron diffraction reveals a significant rotational disorder between the first graphene layer and the SiC surface, although well-defined preferred orientations exist. This is confirmed at the nanometer scale by scanning tunneling microscopy (STM). Finally, STM (at the nm scale) and Raman spectroscopy (at the μm scale) show that the FLG stacking is turbostratic, and that the domain size of the crystallites ranges from 10 to 100 nm. The most striking result is that the FLGs experience a strong compressive stress that is seldom observed for graphene grown on the C face of SiC substrates.
Semiconductors, 2019
Systematic studies of the effect of the electron concentration on the Raman spectra of single-layer graphene films have been carried out. The samples were grown by thermal destruction of the Si-face of the 4H-SiC substrate. Analysis of the results led us to the conclusion that for the correct estimation of the electron concentration and strain values in graphene using Raman spectroscopy data it is necessary to take into account the value of the Fermi velocity in the graphene layer. This conclusion is valid for graphene on any other substrate as well, since the Fermi velocity in graphene depends on the dielectric constant of the substrate.
Epitaxial growth and characterization of graphene on free-standing polycrystalline 3C-SiC
Journal of Applied Physics, 2011
The epitaxial growth of graphene on inexpensive, commercially available, free-standing polycrystalline 3 C-SiC has been achieved by solid state graphitization in ultrahigh vacuum. The structural and electronic properties of such epitaxial graphene (EG) have been explored by Raman spectroscopy, scanning tunneling microscopy (STM), and scanning tunneling spectroscopy (STS). The Raman results show that the grown EG is compressively stressed. The quality of such EG is similar to that on single-crystalline hexagonal SiC substrates. The STM measurements show that the EG grown on polycrystalline SiC presents atomically smooth surfaces across large regions of the underlying SiC substrate with some nanometer-scale features, such as one-dimensional (1-D) ridges, 1-D grain boundaries, and graphene in different stacking sequences. The STS measurements reveal the electronic properties of such EG at an atomic scale. Our approach suggests a more inexpensive way to grow high quality and large scale graphene and represents a promising step toward commercialization of graphene-based electronics.
Layer Number Determination and Thickness-Dependent Properties of Graphene Grown on SiC
IEEE Transactions on Nanotechnology, 2000
The electronic properties of few-layer graphene grown on the carbon-face of silicon carbide (SiC) are found to be strongly dependent on the number of layers. The carrier mobility is larger in thicker graphene because substrate-related scattering is reduced in the higher layers. The carrier density dependence of the mobility is qualitatively different in thin and thick graphene, with the transition occurring at about 2 layers. The mobility increases with carrier density in thick graphene, similar to multilayer graphene exfoliated from natural graphite, suggesting that the individual layers are still electrically coupled in spite of reports recording non-Bernal stacking order in C-face grown graphene. The Hall coefficient peak value is reduced in thick graphene due to the increased density of states. A reliable and rapid characterization tool for the layer number is therefore highly desirable. To date, AFM height determination and Raman scattering are typically used since the optical contrast of graphene on SiC is weak. However, both methods suffer from low throughput. We show that the scanning electron microscopy (SEM) contrast can give similar results with much higher throughput.
Insights into few-layer epitaxial graphene growth on 4H-SiC(0001¯) substrates from STM studies
Physical Review B, 2009
Epitaxial carbon was grown by heating ͑0001͒ silicon carbide ͑SiC͒ to high temperatures ͑1450-1600°C͒ in vacuum. A continuous graphene surface layer was formed at temperatures above 1475°C. X-ray photoelectron spectroscopy ͑XPS͒ and scanning tunneling microscopy ͑STM͒ were extensively used to characterize the quality of the few-layer graphene ͑FLG͒ surface. The XPS studies were useful in confirming the graphitic composition and measuring the thickness of the FLG samples. STM studies revealed a wide variety of nanometer-scale features that include sharp carbon-rich ridges, moiré superlattices, one-dimensional line defects, and grain boundaries. By imaging these features with atomic-scale resolution, considerable insight into the growth mechanisms of FLG on the carbon face of SiC is obtained.